CVE-2019-14902 in Samba
Summary
by MITRE
There is an issue in all samba 4.11.x versions before 4.11.5, all samba 4.10.x versions before 4.10.12 and all samba 4.9.x versions before 4.9.18, where the removal of the right to create or modify a subtree would not automatically be taken away on all domain controllers.
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Analysis
by VulDB Data Team • 03/25/2024
The vulnerability identified as CVE-2019-14902 represents a critical access control flaw within the Samba implementation of Active Directory domain services. This issue affects multiple Samba version lines including 4.11.x before 4.11.5, 4.10.x before 4.10.12, and 4.9.x before 4.9.18, creating a persistent security weakness that undermines the integrity of directory services. The flaw manifests in the improper handling of permission inheritance mechanisms within the Active Directory replication process, specifically when dealing with subtree creation and modification rights. This vulnerability directly impacts the security model of Samba-based domain controllers by allowing unauthorized modification of directory structures even after explicit removal of corresponding permissions.
The technical root cause of this vulnerability lies in the flawed implementation of Access Control List (ACL) inheritance mechanisms during Active Directory replication operations. When administrative rights to create or modify directory subtrees are revoked from users or groups, the system fails to consistently enforce these restrictions across all domain controllers within the replication topology. This inconsistency occurs because the permission removal process does not properly propagate or maintain the updated ACL state throughout the domain controller cluster. The flaw stems from inadequate synchronization of permission states during the replication protocol, particularly when dealing with complex directory structures and nested permissions. This issue falls under CWE-284 which specifically addresses improper access control mechanisms, and aligns with ATT&CK technique T1078.101 which covers valid accounts with restricted access.
The operational impact of this vulnerability is substantial and far-reaching for organizations relying on Samba as their directory service infrastructure. Attackers who can exploit this weakness can potentially bypass access controls and modify directory structures that should be restricted, leading to unauthorized changes in user accounts, group memberships, or even complete directory tree modifications. The vulnerability creates a persistent backdoor that allows malicious actors to maintain access even after administrative attempts to revoke permissions. This flaw particularly affects environments where strict permission controls are essential for compliance requirements, such as financial services, healthcare organizations, or government agencies. The issue becomes more dangerous when combined with other vulnerabilities or when attackers already have some level of access to the domain controller environment, as it provides a mechanism for privilege escalation and persistent access. Organizations may experience unauthorized data modification, unauthorized user creation, or complete compromise of directory service integrity.
Mitigation strategies for CVE-2019-14902 require immediate patching of affected Samba versions to the recommended secure releases including Samba 4.11.5, 4.10.12, or 4.9.18 respectively. Organizations should also implement comprehensive monitoring of directory service access patterns and permission changes to detect potential exploitation attempts. Network segmentation and strict access controls should be enforced to limit exposure of domain controllers to untrusted networks. Regular audits of Active Directory permissions and ACL configurations should be conducted to identify any unauthorized modifications. Additionally, implementing proper change management procedures and ensuring that permission modifications are immediately propagated across all domain controllers will help prevent exploitation of this vulnerability. Security teams should also consider implementing intrusion detection systems specifically configured to monitor for suspicious directory modification activities and unauthorized permission changes within the Active Directory environment.